TBC1D20

At least five mutations in the TBC1D20 gene have been found to cause Warburg micro syndrome, which is the most severe of the disorders caused by RAB18 deficiency. Warburg micro syndrome is characterized by multiple eye abnormalities, vision impairment, severe intellectual disability, and a reduction of the hormones that direct sexual development (hypogonadotropic hypogonadism).

The TBC1D20 gene mutations that cause Warburg micro syndrome eliminate the function of the TBC1D20 protein. Researchers suspect that loss of this protein's function disrupts the normal control of RAB18 activity. It is unclear, though, how the resulting changes in RAB18 activity might lead to eye problems, brain abnormalities, and other features of Warburg micro syndrome.

Because Warburg micro syndrome can be caused by mutations in other genes that disrupt normal RAB18 activity, loss of control of this GTPase is thought to underlie the condition. It is unclear if impaired regulation of RAB1 activity contributes to the features of the condition.

MedlinePlus Genetics provides information about Coloboma